Dense Wavelength Division Multiplexing (DWDM) of optical signals is a technique used to carry many optical signals on a single optical fiber. In DWDM systems, the transmission spectrum, for example 1520 nm to 1550 nm, is divided into many channel wavelengths with adequate spacing left between each channel wavelength to allow for separation of the DWDM signal into its constituent channel wavelengths, also referred to as lambdas, in a demultiplexer, feeding an array of receivers. Each optical signal in the DWDM signal has a unique wavelength representing a particular frequency, which has been assigned to the carrier signal of that channel, the carrier signal having been modulated at a high bit-rate, for example 10 Gb/s, by data to be transmitted on that channel wavelength. This creates optical sidebands above and below the carrier frequency. These determine the densest practical spacing in a WDM system since they must not overlap. As improvements in DWDM related techniques are made, for example improvements in modulation of carrier signals and demultiplexing of DWDM signals into their constituent optical signals, it is feasible that more optical signals, each of a higher bit-rate, will be carried on a single fiber. For example, systems are currently envisioned that will transmit up to 160 channel wavelengths, each carrying up to 10 Gb/s of data, on a single fiber. As these advances are made, switches for switching the DWDM signals will be required to switch a larger number of optical signals both with a granularity of an individual wavelength and as groups of wavelengths, resulting in larger and more complex switch architectures.
With any optical switching system there is a concern of data loss due to a breakdown of the physical path through the optical switching system. The use of DWDM techniques amplifies this concern due to the increased number of channels involved in any physical path breakdown.
In view of the above, there is a need for a protection switching arrangement for optical switching system that addresses the protection requirements of optical switching systems using DWDM techniques described above.